A glow discharge starter is usually connected across or in parallel with an arc discharge lamp and contains a pair of electrodes. At least one of the electrodes comprises a bimetallic element which when heated as a result of the glow discharge bends towards the other electrode, then contact is made the glow discharge ceases causing the bimetallic element to cool and withdraw from the contacted electrode. When contact is broken, a voltage pulse induced by the induction of the ballast appears across the opposed electrodes of the lamp thereby initiating an arc discharge within the lamp. If the lamp ignition does not occur after the first voltage pulse, the glow discharge starter sequence is repeated until lamp ignition occurs.
A glow discharge starter of the aforementioned type is described for example, in the book "Light Sources" by Elenbaas, Philips Technical Library, pages 102-103.
Glow discharge starters are subject to an effect commonly known as dark effect, whereby the breakdown voltage of the glow discharge in the starter is higher in the dark than in the light after a period of non-operation. The above-mentioned effect results in delay at starting and erratic operation.
Several methods are known for reducing the dark effect in glow discharge starters. For example. U.S. Pat. No. 2,332,809, which issued to Peters on Oct. 26, 1943. discloses the use of a coating of a conductive material such as aluminum paint on the inner end of the stem and extending onto the lead-in wires at the points where they emerge from the press.
Other methods employing radioactive materials to help minimize or completely eliminate dark effect are also known. For example. U.S. Pat. No. 2,324,907, which issued to Clack on July 20, 1943 and U.S. Pat. No. 2,740,861 Which issued to Lake et al on Apr. 3, 1956 describe the use of a coating of uranium oxide on the inner surface of the end wall of the glass envelope. A still further attempt of U.S. Pat. No. 2,930,872, which issued to Lake on Mar. 29, 1960 teaches the introduction of a minute quantity of radioactive krypton 85 in addition to an impurity gas such as hydrogen, carbon dioxide or nitrogen. U.S. Pat. No. 2,930,873 which issued to Lake et al on Mar. 29, 1960 suggests introducing tritium and a carrier gas consisting of hydrogen into the gaseous filling of the glow discharge starter. Thorium is also used as a radiation source effective in reducing the dark effect of glow discharge starters.
Disadvantages of the above attempts to neutralize the dark effect include, for instance, substantial increases in material and/or manufacturing costs, severe material licensing requirements in the case of the krypton 85. In the case of the aluminum stem paint the effectiveness thereof decreases during the life of the glow discharge starter thereby rendering the operation of the starter erratic and terminating its useful life.
Glow discharge starters as manufactured, require a period of burning-in commonly referred to as aging, before using with an arc discharge lamp in order to stabilize the voltage characteristics of the starter. The stabilization resulting from such a period of aging is believed to be related to the sputter gettering of materials such as oxygen and water vapor within the glow discharge starter. Sputter cleaning of metal surfaces to promote an oxide-free metal surface for electron emission is also considered to be an important parameter in the aging process. It is highly desirable to have an aging period for the starters as short as . possible in order to be compatible with modern high-speed manufacturing equipment.